#include <stdio.h>  //所有的IO
#include <stdlib.h> //exit() 函数
#include <string.h> //strchr() 函数

#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS  10      // 最大书籍数量

char *s_gets(char *st, int n);
struct book
{
    char title[MAXTITL];
    char author[MAXAUTL];
    float value;
};

int main(int argc, char const *argv[])
{
    struct book library[MAXBKS];    //结构数组
    int count = 0;
    int index, filecount;   //filecount 用于标记原本有的书籍数量
    FILE *pbooks;
    int size = sizeof(struct book);

    if ((pbooks = fopen("../text/book.dat", "a+b")) == NULL) {
        fputs("Can't open book.dat file.\n", stderr);
        exit(1);
    }

    rewind(pbooks);     //定位到文件开始
    while (count < MAXBKS && fread(&library[count], size, 1, pbooks) == 1)  //读到文件末尾退出，返回 NULL
    {
        if (count == 0)
            puts("Current contents of book.dat:");
        printf("%s by %s: $%.2f\n", library[count].title, library[count].author, library[count].value);
        count++;
    }

    filecount = count;  //标记
    if (count == MAXBKS) {
        fputs("The book.dat file is full.", stderr);
        exit(2);
    }

    puts("Please add new book titles.");
    puts("Press [Enter] at the start of a line to stop.");
    while (count < MAXBKS && s_gets(library[count].title, MAXTITL) != NULL && library[count].title[0] != '\0')
    {
        puts("Now enter the author.");
        s_gets(library[count].author, MAXAUTL);
        puts("Now enter the value.");
        scanf("%f", &library[count++].value);
        while (getchar() != '\n')
            continue;   //清理输入行
        if (count < MAXBKS)
            puts("Enter the next title.");
    }

    if (count > 0) {
        puts("Here is the list of your books:");
        for (index = 0; index < count; index++) 
            printf("%s by %s: $%.2f\n", library[index].title, library[index].author, library[index].value);
        fwrite(&library[filecount], size, count - filecount, pbooks);
    }
    else
        puts("No books? To bad.\n");

    puts("Bye.\n");
    fclose(pbooks);

    return 0;
}

char * s_gets(char *st, int n) {
    char *ret_val;
    char *find;

    ret_val = fgets(st, n, stdin);
    if (ret_val) {
        find = strchr(st, '\n');    // 查找换行符
        if (find) {                 // 如果地址不是 NULL
            *find = '\0';           // 替换成空字符
        }
        else {
            while (getchar() != '\n') {
                continue;
            }
        }
    }

    return ret_val;
}
